diff --git a/Python/pystrtod.c b/Python/pystrtod.c
index 30dd4e5..9aeef28 100644
--- a/Python/pystrtod.c
+++ b/Python/pystrtod.c
@@ -718,7 +718,7 @@
 		/* Convert to upper case. */
 		char *p;
 		for (p = buf; *p; p++)
-			*p = toupper(*p);
+			*p = Py_TOUPPER(*p);
 	}
 
 	if (ptype)